In recent years, gas discharge panels, and in particular plasma display panels (PDP), have become widely used a display devices.
PDPs are divided broadly into direct current (DC-type) and alternating current (AC-type), although presently the AC-type, which can adopt a minute cell structure and is suited to high-definition image display, is more prevalent.
An AC-type PDP is structured so that a front panel and a back panel are disposed parallel to and facing each other with a gap therebetween, the panels being sealed together around an outer periphery.
The front panel is structured with display electrodes arranged in a stripe pattern on one main surface of a front glass substrate, a dielectric glass layer covering the display electrodes, and a dielectric protective film (MgO) covering the dielectric glass layer.
On the other hand, the back panel is structured with data electrodes arranged in a stripe pattern on one main surface of a back glass substrate, a dielectric glass layer covering the data electrodes, and barrier ribs provided on the dielectric glass layer in a direction parallel with the data electrodes. Also, red (R), green (G) and blue (B) phosphor layers are formed on the side and bottom surfaces of grooves formed by the dielectric glass layer and the barrier ribs.
The gap between the front panel and the back panel is a discharge space, and this discharge space is filled with a primary gas (rare gas) that acts as a discharge gas. Characteristics demanded of the rare gas include allowing for the radiation of strong ultraviolet rays, the reduction of self-absorption, the reduction of visible light emission, and chemical stability. A mixed gas (Ne—Xe, He—Xe, etc.) and the like having a xenon (Xe) base is generally used in panels as a rare gas that satisfies these conditions. After sealing both panels together around an outer periphery, the discharge space, which has been evacuated to 0.1 mPa, is filled at a required pressure (e.g. 40 kPa to 80 kPa inclusive) with the mixed gas.
In an AC-type PDP having the above structure, each discharge cell can only express the two gradations of on/off. Thus, to display an image in a PDP, an intraframe time-division gradation display method is used, in which a single frame (one field) is divided into a plurality of frames (subfields), and intermediate gradations are expressed by varying the combinations of on/off discharge cells in each subfield. Also, with an AC-type PDP, discharge cells are turned on/off in each subfield using wall charge. Technology relating to this is disclosed, for example, in Japanese patent no. 2756053.
In Japanese patent no. 2756053, the subfields each have (i) a write period in which a write pulse having a selective write voltage lower than a discharge starting voltage is applied between an address electrode (data electrode) and a scan electrode which cross over one another in a pixel to be turned on, thus generating a write discharge for making the pixel emit discharge light, and wall charge as a result of the write discharge, and (ii) a sustain-discharge period in which the pixel selectively written in the write period is made to emit discharge light by applying a sustain pulse having opposite polarity to the wall charge generated by the write discharge and a lower voltage than the discharge starting voltage between the sustain electrodes (as common electrodes X) and all of the scan electrodes (Y1-Yn).
That is, discharge cells in which wall charge has been generated as a result of the write discharge in the write period emit light as a result of the sustain pulse applied in the sustain-discharge period.
However, with the above AC-type PDP, a variety of investigations are being conducted into shortening the write period, with the aim of achieving the high driving speeds that enable lower voltages and higher definition.
In an attempt to solve this problem, improving the characteristics of the dielectric protective film in the front panel of an AC-type PDP, for example, allows electrons to be readily emitted from the film surface, even when an electric field is not applied to the dielectric protective film; that is, the dielectric protective film is made to have a high electron emission ability. A dielectric protective film having a high electron emission ability is necessary for generating gas discharges within discharge cells, and allows for the presence of a large number of initial electrons.
Consequently, with an AC-type PDP having the above dielectric protective film, it is possible to shorten the discharge delay time of write discharges in the write period, and high-speed driving thus becomes possible.
However, when attempts are made to shorten the discharge delay time of the write discharge in the write period of an AC-type PDP, the negative absolute value of the potential of the dielectric protective film surface is reduced as a result of electrons being emitted from the dielectric protective film surface, in the event of electrons, which are charged particles, having accumulated on the film surface as wall charge. That is, the potential of the dielectric protective film surface changes electrically in a positive direction. As a result, the tendency in the above discharge cells is for the absolute amount of negative charge in the wall charge to decrease.
Consequently, even if a sustain pulse is applied to the electrodes in the sustain-discharge period, write errors occur in which discharge cells are not turned on because of the aggregate of wall charge and sustain pulse potential not being able to exceed the discharge starting voltage due to the reduction in wall charge.